Plot result of fourier

Can someone help im trying to plot the fourier spectrum of signal u:

 syms t w

 u=10*sin(t);
 %fourier transform
 four=fourier(u)
 fplot(four)

[boris leung]

using fplot(w,four)

Answer 1

[Newbie]

thank you but why cant i have the analytical solution of the function plotted? Its literally right there in the variable four....

Answer 2

[Star Strider]

See the documentation for the fft (link) function.

[Star Strider]

@Newbie —

It gives the result as:

four =
  -pi*(dirac(w - 1) - dirac(w + 1))*10i

and plots it as a straight line.

You can also try:

syms t w 
u=10*sin(t);
%fourier transform
four = int(u*exp(1j*w*t), t, -1, 1)
four = simplify(four,'Steps',20)
% four = fourier(u)
fplot(real(four), [-15 15])
hold on
fplot(imag(four), [-15 15])
hold off